1. Field of Art
The present invention relates to harvesting machines for collecting crop material from the field, and more particularly to devices installed thereon for continuously measuring the rate of harvested crop material at a particular location in the machine.
2. Description of Prior Art
It is already well known in the art to equip agricultural harvesters with one or more devices for continuously measuring a flow rate of crop material therein. Such devices may comprise a grain flow sensor that measures the quantity of clean grain that is being delivered into a grain tank on the harvester. Their signal may be used for establishing the total yield for a field or a specific yield value for each portion of the field. The latter yield values may be combined with harvester position data from a global positioning system (GPS) sensor and harvester speed data for establishing a specific yield map for a complete field. The grain flow data provided by such devices, however useful they may be for information on the most useful portion of the crop, fail to give an indication on the total yield of the crop vegetation, which also includes straw or, in case of corn harvesting, corn stalks and leafs.
It is also known to monitor the load on one or more components of the harvester for automatically adjusting the settings thereof. Such settings may involve the travel speed of the harvester over the field or the speed of one of the crop processing apparatus inside the harvester, such as the threshing drum speed in case of a combine harvester. A prior art apparatus that has been used for predicting the total load on the crop processing apparatus measures the rate of incoming crop material at the header of a combine harvester. The header is equipped with a transverse auger that conveys cut crop material to the mouth of a straw elevator registering w ith the center of the header. The power required for rotating the auger is proportional to the mass flow rate of the incoming material and can be derived from the force on an idler sprocket in the chain transmission of the auger. A closed vessel, filled with hydraulic oil, and sealed with a rubber sheet was installed below the idler. The idler sprocket was mounted on a lever having an arm that engages the outer surface of the rubber sheet. The pressure of the arm on the sheet and hence the oil pressure in the vessel is directly related to the force on the sprocket and consequently to the torque used for rotating the auger. The pressure in the vessel is measured by an electric pressure transducer, which provides a good indication of the force on the idler sprocket. However this signal suffers from substantial noise caused by the other components of the header. Moreover the lever mounting of the idler was easily jammed by stray straw which accumulated onto and behind the lever.